1. Field of the Invention
The present invention relates to a lens-fitted photographic film unit and an assembling method therefor, and more particularly to a lens-fitted photographic film unit whose unexposed film roll contained in a film supply chamber can be formed properly in a factory.
2. Prior Art
There are widely prevalent lens-fitted photographic film units (hereinafter referred to simply as film units) which have a photographic film and a simple photograph-taking function incorporated therein. Such film units are available at shops at low prices so as to take photographs without the need for carrying about heavy and expensive cameras. These film units are designed to attract customers at low prices not much higher than the price of photographic film cassettes, by providing them with simple structures.
The film units comprise a film housing and an outer casing for imparting a decorative external appearance to the film units. The film housing has a main body provided with a shutter mechanism, a taking lens, a film advancing mechanism and so forth, a front cover attached to the front of the main body and a rear cover attached to the rear of the main body. The main body includes a film take-up chamber for loading a photographic film cassette and a film supply chamber for containing a film roll which is formed by coiling an unexposed photographic film strip which has been drawn out of the photographic film cassette.
FIG. 5 illustrates a conventional way of inserting a film roll 51a in a film supply chamber 50. An unexposed photographic film 51 is wound in a roll about a winding shaft 52 so as to form the film roll 51a in a darkroom of a factory, which roll is then inserted in the film supply chamber 50 by the winding shaft 52. When the winding shaft 52 is withdrawn from the film supply chamber 50, loosening of the film roll 52a occurs so that the upper portion of the film roll 51a rises to impart to the film roll 51a an oval shape. When a rear cover (not shown) is attached to a main body in this condition, the film roll 51a is deformed, and this deformation induces a larger film advancing torque or resistance to advance. In order to eliminate this problem, a pressing jig 53 is used to press the upper portion of the film roll 51a so as to prevent the film roll 51a from ballooning to an oval shape.
Furthermore, when the winding shaft 52 is pulled from the film roll 51a, a side edge of the film roll 51a projects outside the film supply chamber 50 in a spiral, because of the movement of the winding shaft 52. In this condition, the rear cover crushes the projecting side portion, which can result in failure of film advance. For preventing this, upon winding a photographic film 51, the side edge of the film roll 51a is brought into contact with a side edge straightening jig 54 which is initially fitted on the winding shaft 52. The film roll 51a is inserted in the film supply chamber 50 in such a manner that the side edge straightening jig 54 fits into a bottom opening of the film supply chamber 50. The side edge straightening jig 54 is removed after the winding shaft 52 is pulled completely from the film roll 51a.
However, the pressing jig 53 must be removed prior to attaching the rear cover, which causes loosening of the film roll 51a as well. Besides, the diameter of the film roll of a photographic film for 24 frames is different from that of a photographic film for 36 frames, so that it is required to use a different size of pressing jig in each case, which is troublesome and time consuming.
Also, it is necessary to remove the side edge straightening jig 54 after the tendency of the film roll 51a to protrude has been corrected. This is another factor that reduces the speed of assembly. Moreover, when the side edge straightening jig 54 as well as the film roll 51a is inserted in the film supply chamber 50, the side edge straightening jig 54 is brought into contact with the edge of the bottom opening of the film supply chamber 50, which may produce foreign particles since the edge of chamber 50 is rubbed by the side edge straightening jig 54. Especially in the case of photographic film of 24 frames, since the diameter of the film roll is smaller than that of a photographic film of 36 frames, contact pressure between the edge of the bottom opening of the film supply chamber 50 and the side edge straightening jig 54 is high, which increases the chance of foreign particles.